Method for producing amorphous alloy ribbon, and method for producing nano-crystalline alloy ribbon with same

ABSTRACT

An amorphous alloy ribbon free from embrittlement and crystallization and having excellent surface conditions and shape in edge portions is produced by (a) preparing an alloy melt having a composition comprising 13 atomic % or less of B and 15 atomic % or less of at least one selected from the group consisting of transition elements of Groups 4A, 5A and 6A, the balance being substantially Fe; (b) ejecting the alloy melt at a temperature from the melting point of the alloy +50° C. to the melting point of the alloy +250° C. through a nozzle onto the cooling roll rotating at a peripheral speed of 35 m/second or less, a distance between a tip end of the nozzle and the cooling roll being 200 μm or less; (c) starting to supply a gas based on CO 2  to the alloy melt after the surface temperature of the cooling roll has become substantially constant; and (d) grinding the cooling roll while supplying the gas based on CO 2 .

FIELD OF THE INVENTION

The present invention relates to a method for producing an amorphousalloy ribbon having excellent surface conditions and shape in edgeportions, and a method for producing a nano-crystalline alloy ribbonusing such an amorphous alloy ribbon.

PRIOR ART

Liquid-quenching methods are widely known as methods for producingamorphous alloy ribbons for use in magnetic cores, magnetic shields,etc. The liquid-quenching methods include a single roll method, a doubleroll method, a centrifugal method, etc., and preferable among them fromthe aspect of productivity and the maintenance of an apparatus is asingle roll method in which a molten metal is supplied onto a coolingroll rotating at a high speed and rapidly quenched to form an alloyribbon.

FIG. 1 shows one example of apparatuses for carrying out the single rollmethod. An alloy ingot in a crucible 1 is melted by a high-frequencycoil 2, and the resultant alloy melt 3 is ejected through a nozzle 4onto a cooling roll 5 rotating at a high speed and rapidly quenched toform an amorphous alloy ribbon 6. As shown in FIG. 1, for instance, ahigh-pressure gas such as nitrogen, a compressed air, etc. is suppliedfrom a peeling-gas nozzle 7 in an opposite direction to the rotationdirection of the cooling roll 5 immediately after the casting, therebyforcedly peeling the amorphous alloy ribbon 6 from the cooling roll 5.

The amorphous alloy ribbon 6 produced by the above method tends to beprovided with small dents called “air pockets” on a side in contact withthe cooling roll 5. This is because a gas is entrained into a boundarybetween a melt pool portion 10 (hereinafter referred to as “paddle”) andthe cooling roll 5 by the rotation of the cooling roll 5, so that itexpands in the paddle 10 until the melt is solidified. Because theformation of such air pockets leads to the roughing of a surface of theribbon 6, the air pockets should be as few as possible.

Proposed by German Patent DD266046A1, Japanese Patent Laid-Open No.6-292950, etc. to suppress the formation of air pockets is a method inwhich a CO₂ gas is supplied to the paddle in various directions. Thismethod is advantageous in that it can suppress the formation of airpockets to reduce the surface roughness of a ribbon on a side in contactwith the cooling roll.

Alternatively, Japanese Patent Laid-Open No. 59-209457, Japanese PatentPublication No. 1-501924, etc. propose a method for producing anamorphous alloy ribbon in vacuum or in a He atmosphere, a method forproducing an amorphous alloy ribbon while flowing a gas having a lowerdensity than the air at normal temperature, such as a heated CO gas, aHe gas at normal temperature etc., to the paddle from rearward. Why theformation of air pockets can be suppressed by these methods seems to bethe fact that a gas entrained by the rotation of the cooling roll has areduced density, resulting in decrease in the kinetic pressure of thegas impinging on the paddle, thereby suppressing the vibration of thepaddle.

Among the above methods, the method of flowing a CO₂ gas to the paddlefrom rearward (from a side opposite to the side on which the ribbon isformed) is suitable for the mass production of amorphous alloy ribbonsfrom the aspect of production cost and safety.

The total length of an amorphous alloy ribbon continuously produced inone casting lot by a liquid-quenching method generally exceeds 3,000 m.When the resultant amorphous alloy ribbon is wound around a reel afterthe completion of casting, the ribbon is likely to be twisted.Accordingly, the quenched ribbon should continuously be woundimmediately after peeling from the cooling roll.

For instance, Japanese Patent Laid-Open Nos. 8-318352 and 11-188458disclose a method in which a magnetized reel rotating in an oppositedirection to a cooling roll is positioned near the cooling roll tomagnetically attract the peeled ribbon, which is continuously woundaround the reel.

It is also known that the heat treatment of an amorphous alloy ribbonproduced by the above-described methods at a temperature equal to orhigher than the crystallization temperature of the alloy can provide anano-crystalline alloy ribbon having an average particle size of 100 nmor less. Typical alloys capable of forming nano-crystalline alloyribbons are Fe—Si—B—(Nb, Ti, Hf, Mo, W, Ta)—Cu alloys, Fe—(Co,Ni)—Cu—Si—B—(Nb, W, Ta, Zr, Hf, Ti, Mo) alloys, Fe—(Hf, Nb, Zr)—Balloys, Fe—Cu—(Hf, Nb, Zr)—B alloys, etc. described in Japanese PatentPublication Nos. 4-4393 and 7-74419, Japanese Patent 2,812,574, etc.

The nano-crystalline alloys are not only substantially free from thermalinstability unlike the amorphous alloy, but also are subjected to lesschange with time and have lower magnetostriction and higher permeabilitythan the amorphous alloys, they are used for common-mode choke coils,pulse transformers, leakage breakers, etc.

As a result of experiment to produce an amorphous alloy ribbon 6 using alaboratory-scale apparatus whose casting time is less than 30 secondswhile flowing a CO₂ gas, the resultant ribbon had excellent surfaceconditions. However, in a production experiment using amass-production-scale apparatus, it was found that as the casting timepassed, there arose the problems of embrittlement and crystallization inthe formed amorphous alloy ribbon that were not observed in the shortcasting process, though the surface conditions of the amorphous alloyribbon was improved by the supply of a CO₂ gas. In addition to theseproblems, it has also be found that a new problem of serrated irregularshapes in their edge portions takes place. This phenomenon never occurseven in the long casting process of an amorphous alloy ribbon unless aCO₂ gas is supplied.

Because the total length of an amorphous alloy ribbon continuouslyproduced in one casting step by a mass-production apparatus exceeds3,000 m, the amorphous alloy ribbon is continuously wound around a largereel during the casting from the aspect of efficiency. The ribbon isthen divided to proper length that can easily be handled to producewound cores, etc., and wound around a large number of small reels. Atthis time, if the ribbon had a serrated irregular shape in its edgeportions, the edge portion of the ribbon engages a reel, resulting inextreme difficulty in handling.

The irregular shape of the ribbon in its edge portions also posesinconveniences in the production of a wound core. In the continuousproduction of a wound core from a ribbon, the winding of the ribbon isoften carried out with the edge portions of the ribbon abutting againsta plate to make the resultant wound core have a constant height. In thiscase, too, if the ribbon had a serrated irregular shape in its edgeportions, the ribbon engages the abutting plate, thereby making theproduction of a wound core difficult.

If the ribbon were brittle, breakage, cracking, etc. would be likely tooccur in the production of wound cores and laminated cores. In addition,if the ribbon contains coarse crystals, it would have large crystalmagnetic anisotropy, resulting in the deterioration of its soft magneticproperties. Further, if an amorphous alloy ribbon having coarse crystalswere heat-treated at a temperature equal to or higher than thecrystallization temperature of the alloy, the resultant nano-crystallinealloy ribbon would have deteriorated soft magnetic properties.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodfor continuously producing an amorphous alloy ribbon having improvedsurface conditions on a side in contact with a cooling roll andexcellent edge shapes, free from embrittlement and crystallization.

Another object of the present invention is to provide a method forproducing a nano-crystalline alloy ribbon by heat-treating such anamorphous alloy ribbon.

DISCLOSURE OF THE INVENTION

As a result of investigating problems such as irregular edge shapes,embrittlement and crystallization occurring as the amount of a ribboncast increases (as casting continues longer) in the production of anamorphous alloy ribbon with a CO₂ gas supplied, the inventors have foundthat the above problems can be overcome by grinding a cooling rollduring the casting. The present invention has been completed based onthis finding.

Thus, the method for producing an amorphous alloy ribbon by ejecting analloy melt onto a cooling roll and rapidly quenching it according to thepresent invention comprises carrying out the grinding of the coolingroll while supplying a gas based on CO₂ near a paddle of said alloy meltduring the casting.

The alloy used in the present invention preferably has a compositioncomprising 13 atomic % or less of B and 15 atomic % or less of at leastone selected from the group consisting of transition elements of Groups4A, 5A and 6A, the balance being substantially Fe. Also, when theamorphous alloy ribbon is to be heat-treated for nano-crystallization,the alloy melt preferably contains 3 atomic % or less of at least one ofCu, Ag and Au.

When a gas based on CO₂ is supplied near a paddle of an alloy meltejected from a nozzle onto a cooling roll immediately after the start ofcasting, the ribbon tends to be broken. However, when the gas based onCO₂ starts to be supplied after the surface temperature of the coolingroll has become substantially constant, the possibility of the breakageof the ribbon substantially decreases. Here, “surface temperature hasbecome substantially constant” means that the variation range of thesurface temperature of the cooling roll has become within 10° C.relative to its average temperature. Though the surface temperature ofthe cooling roll generally starts to elevate immediately after the startof casting, it becomes substantially constant in several seconds to tenand several seconds because heat from the alloy melt gets balanced withheat dissipating from the cooling roll.

The peripheral speed of the cooling roll is preferably 35 m/second orless, more preferably 20-30 m/second. The temperature of the alloy meltis preferably from the melting point of the alloy +50° C. to the meltingpoint of the alloy +250° C., more preferably from the melting point ofthe alloy +100° C. to the melting point of the alloy +200° C. Inaddition, the distance from a tip end of a nozzle to a cooling roll ispreferably 200 μm or less, more preferably 100-180 μm, furtherpreferably 100-150 μm. Under such casting conditions, it is possible tostably produce an amorphous alloy ribbon having a thickness of 8-25 μm,particularly 8-19 μm.

The preferred method of the present invention for producing an amorphousalloy ribbon by ejecting an alloy melt onto a cooling roll and rapidlyquenching it comprises (a) preparing an alloy melt having a compositioncomprising 13 atomic % or less of B and 15 atomic % or less of at leastone selected from the group consisting of transition elements of Groups4A, 5A and 6A, the balance being substantially Fe; (b) ejecting thealloy melt at a temperature from the melting point of the alloy +50° C.to the melting point of the alloy +250° C. through a nozzle onto thecooling roll rotating at a peripheral speed of 35 m/second or less, adistance between a tip end of the nozzle and the cooling roll being 200μm or less; (c) starting to supply a gas based on CO₂ to the alloy meltafter the surface temperature of the cooling roll has becomesubstantially constant; and (d) grinding the cooling roll whilesupplying the gas based on CO₂.

The heat treatment of the amorphous alloy ribbon produced by the abovemethod at a temperature equal to or higher than the crystallizationtemperature of the alloy can provide a nano-crystalline alloy ribbonhaving a nano-crystalline structure having an average particle size of100 nm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing one example of an apparatus forcarrying out the method of the present invention for producing anamorphous alloy ribbon;

FIG. 2 is a partial cross-sectional view showing one example of a CO₂gas-blowing nozzle in the apparatus of FIG. 1;

FIG. 3 is an electron photomicrograph showing an edge portion of theamorphous alloy ribbon of EXAMPLE 2;

FIG. 4 is an electron photomicrograph showing an edge portion of theamorphous alloy ribbon of COMPARATIVE EXAMPLE 3;

FIG. 5 is an electron photomicrograph showing an edge portion of theamorphous alloy ribbon of COMPARATIVE EXAMPLE 4;

FIG. 6 is an electron photomicrograph showing an edge portion of theamorphous alloy ribbon of EXAMPLE 4;

FIG. 7 is an electron photomicrograph showing an edge portion of theamorphous alloy ribbon of COMPARATIVE EXAMPLE 7;

FIG. 8 is a scanning electron photomicrograph showing an edge portion ofthe amorphous alloy ribbon of EXAMPLE 24; and

FIG. 9 is a scanning electron photomicrograph showing an edge portion ofthe amorphous alloy ribbon of EXAMPLE 25.

DESCRIPTION OF PREFERRED EMBODIMENTS

[1] Supply of CO₂ Gas and the Grinding of the Cooling Roll

An important feature of the present invention is that the grinding ofthe cooling roll is carried out while supplying a gas based on CO₂, inthe production process of an amorphous alloy ribbon for a long period oftime. The gas based on CO₂ is a pure CO₂ gas or a mixture of a CO₂ gasand another gas, and another gas should not exert adverse effects on theresultant amorphous alloy ribbon.

As a result of investigation of the problems inherent in the casting ofan amorphous alloy ribbon in the presence of a CO₂ gas for a long periodof time, it has been found that the influence of the deterioration ofthe surface roughness of a cooling roll on the ability of the coolingroll to cool a melt is extremely larger when a CO₂ gas is suppliedduring the casting than when no CO₂ gas is supplied, and that thedeterioration of the surface roughness of the cooling roll also affectsthe shape of resultant ribbon in its edge portions. The deterioration ofthe surface roughness of the cooling roll is caused by the formation ofdents by incessant impingement by a high-temperature melt, the adhesionof an alloy to the surface of the cooling roll, etc.

Further, to investigate the surface roughness of a cooling rollnecessary for avoiding the above problems, comparison has been carriedout on the surface roughness of cooling rolls according to JIS B 0601.As a result, it has been found that good amorphous alloy ribbons areobtained, when the cooling roll is ground such that it has an averagesurface roughness Ra of 0.5 μm or less and a ten-point average surfaceroughness Rz of 4 μm or less during the casting. It has also been foundthat better ribbons are obtained by having the cooling roll keep anaverage surface roughness Ra of 0.3 μm or less and a ten-point averagesurface roughness Rz of 2 μm or less.

Investigation and consideration will be given in detail below withrespect to the influence of the supply of a CO₂ gas and the grinding ofthe cooling roll on the edge shape, embrittlement and crystallization ofthe resultant amorphous alloy ribbon, and the reasons why the grindingof the cooling roll should be carried out while supplying a CO₂ gas.

(1) Embrittlement and Crystallization of Ribbon

When an amorphous alloy ribbon is produced by a mass-production-scaleapparatus for a long period of time while supplying a CO₂ gas withoutgrinding the cooling roll, the cast amorphous alloy ribbon tends tosuffer from extreme embrittlement and crystallization. On the otherhand, when a CO₂ gas is supplied while grinding the cooling roll,substantially no embrittlement and crystallization take place in theamorphous alloy ribbon even after a long period of casting by amass-production-scale apparatus.

(2) Shape of Ribbon Edge

When the amorphous alloy ribbon is cast by a mass-production-scaleapparatus for a long period of time while supplying a CO₂ gas withoutgrinding the cooling roll, extreme irregularity such as serration occursin the shape of ribbon edges as the casting process proceeds. Theserrated shape in the edge portions of the cast amorphous alloy ribbonbecomes increasingly remarkable as the casting time passes. On the otherhand, when a CO₂ gas is supplied with the cooling roll ground,substantially no irregular shapes are formed in ribbon edges even in thelong casting process. Thus, the problems caused by the supply of a CO₂gas can be overcome by grinding the cooling roll during the casting of aribbon.

The first reason why the air pockets of an alloy melt decrease by a CO₂gas is the thermal decomposition of the CO₂ gas. When the CO₂ gas isbrought into contact with an alloy melt in the shape of a ribbon ejectedfrom a nozzle, CO₂ is thermal decomposed by the heat of the alloy meltto generate CO and O₂, thereby forming a uniform oxide layer on thepaddle surface. As a result, the viscosity of the paddle increases,thereby suppressing the vibration of the paddle. This in turn makes itdifficult to entrain a CO₂ gas in the paddle, resulting in decrease inair pockets.

The second reason is that a CO₂ gas has larger specific heat than theair, nitrogen, etc. With the cooling roll subjected to contact andfriction with a high-temperature melt, the cooling roll surface isroughened, and a gas highly tends to be entrained into a paddle by therotation of the cooling roll. In such a case, air pockets are unlikelyto be formed in the presence of a CO₂ gas, because a CO₂ gas having alarge specific heat is not so much thermally expanded in the paddle asother gases.

Though a CO₂ gas had the above advantage, it is more heated by radiantheat from the paddle than the air and nitrogen, because it has largeheat absorption than the air and nitrogen. Therefore, the CO₂ gasentrained into a boundary between the paddle and the cooling roll is ata higher temperature than the air and nitrogen. With a high-temperatureCO₂ gas entrained into the above boundary, it is presumed that thecooling speed of the ribbon on the cooling roll is lowered, making itmore likely to cause embrittlement and crystallization in the ribbon.

With dents on the cooling roll surface, the gas is likelier to beentrained in the paddle, and particularly in the case of using a CO₂ gashaving large heat absorption, the formation of dents on the cooling rolldirectly leads to increase in the embrittlement and crystallization ofthe ribbon. Therefore, the suppression of the formation of dents on thecooling roll surface is important to reduce air pockets by a CO₂ gas inthe long casting process of an amorphous alloy ribbon, and to suppressthe embrittlement and crystallization of the amorphous alloy ribbon thatstart to occur after the surface temperature of the cooling roll hasbecome substantially constant.

It is generally known that the kinetic pressure of a gas is proportionalto the square of the specific gravity of a gas. When a CO₂ gas having alarger specific gravity than the air, nitrogen, etc. impinges on apaddle, the momentum of the CO₂ gas to the paddle 10 is extremely largerthan that of the air, etc. Taking a nitrogen gas having a specificgravity of 1.1 and a CO₂ gas having a specific gravity of 1.8 at 300 Kfor instance, the kinetic pressure of the CO₂ gas is about 2.7 timesthat of nitrogen at the same flow rate at 300 K.

When there are few dents on the surface of a cooling roll 5 with littleentrainment of a gas into the paddle 10, no problem is caused by a largemomentum given by the CO₂ gas in FIG. 2. However, in a state where alarge number of dents are formed on the cooling roll 5, a large amountof a CO₂ gas is entrained into the paddle 10. In this case, it ispresumed that the paddle 10 is likely to be vibrated because of a largemomentum of a CO₂ gas, resulting in irregularities such as serration inthe shape of edge portions of the resultant amorphous alloy ribbon.Accordingly, to suppress irregularities such as serration in the shapeof edge portions of the ribbon that occurs when using a CO₂ gas, it isimportant to suppress dents of the cooling roll 5, which increase as thecasting time passes.

Because the cooling roll 5 without deteriorated surface roughness isfree from the above problems, the grinding of the cooling roll 5 maystart at any time during the casting process. Also, though the grindingmay be carried out intermittently with a certain interval, it ispreferably carried out continuously from the aspect of easiness ofcontrol.

Though the grinding of the cooling roll may be conducted with grindingpapers, it is preferably carried out with a brush that does not generatedust, because the insufficient collection of dust generated by grindingcauses such problem that pores, etc. are formed in the ribbon. As shownin FIG. 2, it is preferable to use as a brush 11 a roll-shaped wirebrush rotating in the same direction as the cooling roll 5. The rotationspeed of the brush 11 is preferably ⅓ or less, particularly {fraction(1/10)}-⅕, of the peripheral speed of the cooling roll 5.

When the brush 11 used for grinding is too hard, the surface of thecooling roll 5 is deeply scratched by grinding, resulting in suchproblems as the breakage of the ribbon 6 during the casting and decreasein the improvement of surface roughness of the cooling roll 5.Accordingly, the brush 11 for grinding preferably has the same hardnessor less as that of the cooling roll 5. Such brush 11 is preferablyconstituted by thin wires of stainless steel, brass, copper, etc. Eachwire for the brush 11 preferably has a diameter of 0.03-0.1 mm.

The materials of the cooling roll 5 are preferably alloys having highthermal conductivity, such as Cu, Cu—Be alloys, Cu−Cr alloys, etc. Also,when a cooling medium such as water, etc. is caused to flow in thecooling roll 5 in a circumferential or axial direction, the control ofthe surface temperature of the cooling roll 5 becomes easier.

[2] Amorphous Alloy Ribbon

(1) Alloy Composition

The alloy to which the method of the present invention is applicablecontains B from the aspect of capability of forming an amorphousstructure. However, an excessively large content of B not only leads tothe embrittlement and decrease in a magnetic flux density of anamorphous alloy ribbon, but also causes the problem of a higher costbecause B is an expensive element. Accordingly, the content of B ispreferably 13 atomic % or less. The more preferred content of B 4-13atomic %.

Particularly in the case of an Fe-based amorphous alloy for forming anano-crystalline alloy, the content of B is preferably 10 atomic % orless, more preferably 4-10 atomic %. With the content of B of 10 atomic% or less, magnetically hard compounds such as Fe₃B and Fe₂B that hinderthe movement of magnetic domain walls are difficult to be precipitatedbecause of a nano-crystalline structure in the heat treatment, therebymaking it likely to obtain a uniform nano-crystalline structure based ona bcc-Fe solid solution.

The transition elements of Groups 4A, 5A and 6A are effective for theadjustment of magnetostriction and the improvement of permeability of anamorphous alloy. The preferred transition elements in Groups 4A, 5A and6A are Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. These elements areconcentrated in an amorphous phase remaining around bcc-Fe crystalgrains formed in the heat treatment of an amorphous alloy ribbon at atemperature equal to or higher than the crystallization temperature ofthe alloy, thereby stabilizing the remaining amorphous phase and thussuppressing the growth of bcc-Fe crystal grains.

The amount of at least one of these transition elements added ispreferably 15 atomic % or less. When the amount of the transitionelement added exceeds 15 atomic %, embrittlement and decrease in amagnetic flux density are likely to occur in the amorphous alloy ribbon.Though the effect of suppressing the formation of bcc-Fe crystal grainsdiffers depending on elements, the preferred content of the transitionelement is 1-10 atomic %.

When at least one of Cu, Ag and Au is added to the amorphous alloyribbon together with at least one of elements of Groups 4A, 5A and 6A,the number of primary crystal nuclei precipitated increases in the heattreatment at a temperature equal to or higher than the crystallizationtemperature of the alloy, thereby making the precipitated crystal grainsfiner. The amount of at least one of Cu, Ag and Au added is preferably 3atomic % or less. When the amount of this element added exceeds 3 atomic%, the resultant amorphous alloy ribbon becomes brittle. Because Cu, Agand Au are elements that are easily separated from Fe, they would beseparated from Fe even with a liquid-quenching method, failing to obtaina uniform solid solution, if their contents are excessive. Incidentally,the lower limits of the amounts of Cu, Ag and Au added are preferably0.1 atomic % for each.

(2) Production Method

The method of the present invention for producing an amorphous alloyribbon is characterized by carrying out the grinding of the cooling rollwhile supplying a gas based on CO₂ near a paddle of an alloy meltejected onto the cooling roll.

When the gas based on CO₂ is supplied to a paddle 10 in FIG. 2, there isa large likelihood that the amorphous alloy ribbon 6 is broken at theinitial stage of casting. As a result of investigation of a ribbon 6broken at the very initial stage of casting with a CO₂ gas suppliedsince before the start of casting, it has been found that the breakageof the ribbon 6 occurs while the ribbon 6 is still on the cooling roll5, and that no cracking and breakage occur in the edge portions of theribbon 6 after winding.

Because the surface temperature of a cooling roll is unstable severalseconds to ten and several seconds after the start of casting,regardless of whether or not a CO₂ gas is supplied to improve thesurface conditions of the ribbon 6, the paddle 10 does not have a stableshape. Accordingly, the ribbon 6 obtained immediately after the start ofcasting tends to be relatively thin and weak and have a large number ofpores, etc., whereby it is easily broken.

Because the supply of a gas based on CO₂ to a paddle 10 immediatelyafter the start of casting leads to decrease in air pockets generated inthe ribbon 6 on a side in contact with the cooling roll 5, a melt and asolidified ribbon 6 are in direct contact with the cooling roll 5 in alarger area, resulting in a higher cooling speed of the ribbon 6. As aresult, the solidified ribbon 6 is subjected to rapid thermal shrinkage,undergoing higher internal stress than when a gas based on CO₂ is notsupplied. This seems to be why cracking and breakage are observed inedge portions of the ribbon 6 after winding. It is thus presumed thathigh stress in the ribbon 6 results in higher likelihood of breakage.

For the reasons described above, to prevent the ribbon 6 from beingbroken at the initial stage of casting, it is effective to startsupplying a gas based on CO₂ near a paddle of the alloy melt, after thesurface temperature of the cooling roll 5 becomes constant and the stateof the ribbon 6 is stabilized.

The peripheral speed of the cooling roll 5 is preferably 35 m/second orless. With the peripheral speed of the cooling roll 5 set at 35 m/secondor less, the ribbon 6 can be provided with improved surface conditionsand shape in its edge portions. Particularly the shape of the ribbon 6in edge portions can remarkably be improved. Though thinner ribbons areusually cast at higher roll peripheral speed than thicker ribbons, theperipheral speed of the cooling roll 5 is preferably as low as possibleeven for thin ribbons from the aspect of easiness of control. In thissense, the peripheral speed of the cooling roll 5 is more preferably20-30 m/second, particularly preferably 27-30 m/second.

The temperature of a melt is preferably from the melting point of itsalloy +50° C. to the melting point of its alloy +250° C. When thetemperature of a melt is lower than the melting point of its alloy +50°C., the nozzle 4 tends to be clogged. On the other hand, when thetemperature of the melt is higher than the melting point of its alloy+250° C., the cooling speed of the melt is slow near the solidificationtemperature of the melt, resulting in the brittleness andcrystallization of alloy ribbons. The high melt temperature alsoprovides the resultant alloy ribbons with rough surface because of largewear of the cooling roll 5. The more preferred temperature of the meltis from the melting point of its alloy +100° C. to the melting point ofits alloy +200° C.

The distance D between the tip end of the melt-ejecting nozzle 4 and thecooling roll 5 is preferably 200 μm or less. When a thin ribbon isproduced at a low peripheral speed, it is preferable to reduce the sizeof a slit of the melt-ejecting nozzle 4 or the distance D between themelt-ejecting nozzle 4 and the cooling roll 5. The more preferreddistance D is 100-180 μm, particularly 100-150 μm.

As shown in FIG. 2, the position of a nozzle 9 blowing a gas based onCO₂ is preferably on the upstream side of the melt-ejecting nozzle 4.Here, “on the upstream side of a nozzle 4” means a front side in adirection of the relative movement of the nozzle 4 to the cooling roll5. The ejection direction of a CO₂ gas, which is identical to thedirection of the nozzle 9, is preferably the radial direction of thecooling roll 5.

Also, the ejection direction of a gas based on CO₂ is preferably setsubstantially upstream of the paddle. With the ejection of a gas basedon CO₂ directed to the cooling roll 5 substantially upstream of thepaddle 10, the conditions of the ribbon 6 on a freely solidified surfaceare improved, and the formation of air pockets are more remarkablysuppressed, than when the gas is directly supplied to the tip end of thenozzle 4 or to the paddle 10.

(3) Amorphous Alloy Ribbon

In the amorphous alloy ribbon produced under the above conditions,substantially no α-Fe crystal phase is precipitated. Crystalsprecipitated in the amorphous alloy ribbon because of improper castingconditions are those in the form of dendrite as large as 0.2-1 μm inparticle size not nano-crystalline, which are much larger than finecrystals precipitated from the amorphous phase by the heat treatment.The existence of such large crystals makes the nano-crystallinestructure obtained by the heat treatment non-uniform, resulting inlarger crystal magnetic anisotropy and thus deteriorated magneticproperties of the nano-crystalline alloy ribbon.

The method of the present invention can generally provide an amorphousalloy ribbon having a thickness in a range of 8-25 μm. Particularly evenat a thickness of 19 μm or less, the amorphous alloy ribbon obtained bythe present invention has excellent surface conditions and shape in edgeportions. In addition, the method of the present invention is suitablefor stably producing an amorphous alloy ribbon having a length of about3,000 m or more and excellent surface conditions and shape in edgeportions.

[3] Nano-Crystalline Alloy Ribbon

The amorphous alloy ribbon 6 with low crystallinity obtained by themethod of the present invention can be converted to a nano-crystallinealloy ribbon by a heat treatment. Here, “nano-crystalline” means a metalstructure containing fine crystals having an average particle size of100 nm or less.

As described above, to obtain a nano-crystalline alloy ribbon withexcellent magnetic properties, it is important that the amorphous alloyribbon 6 to be heat-treated should not contain coarse crystals. This isbecause the slightest amount of course crystals in the amorphous alloyribbon 6 to be heat-treated causes extreme deterioration in magneticproperties in a nano-crystalline alloy ribbon obtained by a heattreatment at a crystallization temperature or higher.

The heat treatment for obtaining a nano-crystalline alloy ribboncomprises heating at 400-700° C. for 1 minute to 24 hours. When the heattreatment temperature is lower than 400° C., fine crystallization cannotsubstantially be achieved. On the other hand, when it exceeds 700° C.,coarse crystal grains are likely to be precipitated. The preferred heattreatment temperature is 500-650° C. Though the heat treatment time mayvary depending on the heat treatment temperature, the heat treatmenttime of less than 1 minute generally fails to achieve the stableprecipitation of fine crystals. On the other hand, when it exceeds 24hours, only low production efficiency of forming a nano-crystallinealloy ribbon can be achieved. Incidentally, because the heat treatmentof the amorphous alloy ribbon in the air oxidizes a ribbon surface,resulting in deterioration in the magnetic properties of the resultantnano-crystalline alloy ribbon, the heat treatment is preferably carriedout in an inert atmosphere such as nitrogen, argon, etc.

The present invention will be described in detail referring to EXAMPLESbelow without intention of limiting the present invention thereto.

EXAMPLES 1 and 2, COMPARATIVE EXAMPLES 1-4

Production and Evaluation of Amorphous Alloy Ribbon

An ingot of an Fe-based alloy having a composition ofCu₁Nb_(2.5)Si_(13.5)B₇Fe_(bal.) by atomic % was introduced into acrucible 1 shown in FIG. 1, and melted by induction heating by ahigh-frequency coil 2. The resultant alloy melt 3 was ejected onto acooling roll 5 made of a Cu—Be alloy and rapidly quenched under theconditions shown in Table 1 below, to form an amorphous alloy ribbon 6of EXAMPLE 1 having a width of 30 mm and a thickness of 19 μm.

TABLE 1 Casting Conditions Temperature of melt 3 1,350° C. Peripheralspeed of cooling roll 5 27 m/second Distance D between tip end of 120 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas30 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.06-mm-diameter brass wire brush Distance L between paddle 10 and 15 mmorifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂ gas-blowing40 mm in width direction of nozzle 9 cooling roll 5 and 1 mm in rotationdirection of cooling roll 5

As shown in FIG. 1, the resultant amorphous alloy ribbon 6 was caused topeel off from the cooling roll 5 by supplying a nitrogen gas from anozzle 7 onto the cooling roll 5 in an opposite direction to therotation direction of the cooling roll 5, and a reel 8 having apermanent magnet embedded therein and rotating in an opposite directionto the rotation direction of the cooling roll 5 was brought close to thecooling roll 5 to wind the amorphous alloy ribbon 6. The winding of theamorphous alloy ribbon 6 onto the reel 8 was started after about 2seconds from the start of casting.

Portions of the resultant amorphous alloy ribbon were taken as sampleswhen 1 minute passed from the start of casting, and when 10 minutespassed from the start of casting, respectively. The samples of EXAMPLE 1and COMPARATIVE EXAMPLES 1 and 2 were ribbon portions obtained when 1minute passed from the start of casting, and the samples of EXAMPLE 2and COMPARATIVE EXAMPLES 3 and 4 were ribbon portions obtained when 10minutes passed from the start of casting.

Incidentally, the grinding of the cooling roll 5 was carried out, whilesupplying a CO₂ gas and rotating a brush 11 in the same direction as thecooling roll 5 in the production process of the ribbon 6 of EXAMPLES 1and 2. The grinding of the cooling roll 5 was not carried out in theproduction process of the ribbon 6 of COMPARATIVE EXAMPLES 1 and 3,though a CO₂ gas was supplied. The supply of a CO₂ gas and the grindingof the cooling roll 5 were not carried out in the production process ofthe ribbon 6 of COMPARATIVE EXAMPLES 2 and 4.

With respect to each of the resultant ribbons, an average surfaceroughness Ra on both of the freely solidified surface and the surface incontact with the cooling roll 5, the presence of crystals andembrittlement were examined. The average surface roughness Ra wasmeasured according to JIS B 0601. The presence of crystals was evaluatedby the intensity of a peak of α-Fe (200) in the X-ray diffractionpattern of each ribbon. The presence of embrittlement was evaluated bycracking caused by a 180° bending test according to JIS Z 2248. Inaddition to the above items, a reflection electron image of an edgeportion of each ribbon was taken using a scanning electron micrograph toevaluate the serrated irregularities of the edge portion.

The evaluation results of the amorphous alloy ribbons of EXAMPLE 1 andCOMPARATIVE EXAMPLES 1 and 2 are shown in Tables 2 and 3. As is clearfrom Table 2, when 1 minute passed from the start of casting, theribbons of EXAMPLE 1 and COMPARATIVE EXAMPLE 1 produced while supplyinga CO₂ gas had substantially the same surface roughness, which wassmaller than that of the ribbon of COMPARATIVE EXAMPLE 2 producedwithout supplying a CO₂ gas, regardless of whether or not the grindingof the cooling roll 5 was carried out. With respect to embrittlement,crystallization and edge shape, there were no appreciable differencesbetween the ribbon of EXAMPLE 1 and those of COMPARATIVE EXAMPLES 1 and2.

As is clear from Table 3, when 10 minutes passed from the start ofcasting, too, the ribbons 6 of EXAMPLE 2 and COMPARATIVE EXAMPLE 3produced while supplying a CO₂ gas, regardless of whether or not thegrinding of the cooling roll 5 was carried out, had substantially thesame surface roughness, which was extremely smaller than that of theribbon of COMPARATIVE EXAMPLE 4. However, it was confirmed that theribbon 6 of COMPARATIVE EXAMPLE 3 produced only by supplying a CO₂ gaswithout grinding the cooling roll 5 was poorer than the ribbon ofEXAMPLE 2 in crystallization, embrittlement and edge shape. On the otherhand, the ribbon 6 of EXAMPLE 2 produced by carrying out the grinding ofthe cooling roll 5 during the casting was clearly improved incrystallization, embrittlement and edge shape.

The electron photomicrographs of the amorphous alloy ribbons 6 ofEXAMPLE 2 and COMPARATIVE EXAMPLES 3 and 4 in their edge portions areshown in FIGS. 3, 4 and 5. As is clear from FIGS. 3 and 4, the ribbon ofEXAMPLE 2 produced while supplying a CO₂ gas and grinding the coolingroll 5 was flatter in a shape in edge portions than the ribbon ofCOMPARATIVE EXAMPLE 3 produced while supplying a CO₂ gas withoutgrinding the cooling roll 5. Also, as is clear from FIG. 5, the ribbonof COMPARATIVE EXAMPLE 4 produced without supplying a CO₂ gas was rifewith air pockets, though it had a flat edge shape.

Production and Evaluation of Nano-Crystalline Alloy Ribbon

Using the same amorphous alloy ribbon portions as above, wound coreseach having an outer diameter 20 mm and an inner diameter of 15 mm wereproduced, and then heat-treated at 550° C. for 60 minutes to form woundcores of nano-crystalline alloy ribbons. Each of the resultantnano-crystalline alloy ribbons was measured with respect to an initialpermeability at a frequency of 1 kHz. The results are shown in Tables 2and 3. As is clear from Tables 2 and 3, a nano-crystalline alloy ribbonhaving excellent soft magnetic properties could be produced stably for along period of time from an amorphous alloy ribbon 6 cast whilesupplying a CO₂ gas and grinding the cooling roll 5.

The observation of the metal structure of the nano-crystalline alloyribbon with a transmission electron micrograph revealed that in a casewhere nano-crystalline alloy ribbons were obtained from the amorphousalloy ribbon portion of EXAMPLE 1 obtained when 1 minute passed from thestart of casting and the amorphous alloy ribbon portion of EXAMPLE 2obtained when 10 minutes passed, respectively, both of them had anaverage particle size of about 20 nm. The nano-crystalline alloy ribbonsof COMPARATIVE EXAMPLES 1 and 2 also had an average particle size ofabout 20 nm, as long as they were obtained from the amorphous alloyribbon portions obtained when 1 minute passed from the start of casting.However, crystal particles exceeding a particle size of 0.1 μm wereobserved in the nano-crystalline alloy ribbons of COMPARATIVE EXAMPLES 3and 4 obtained from the amorphous alloy ribbon portions obtained when 10minutes passed from the start of casting.

TABLE 2 When 1 minute passed from the start of casting ProductionAverage Surface Intensity of α (200) Conditions Roughness Ra (μm) Peak(cps) Supply Freely Surface in Freely Surface in of CO₂ GrindingSolidified Contact Solidified Contact with Shape in Edge Cracking byInitial Permeability No. Gas of Roll Surface with Roll Surface RollPortion Bending Test after Heat Treatment EXAMPLE Yes Yes 0.27 0.23 0 0◯ No 162,700 1 COM. EX. Yes No 0.28 0.22 0 0 ◯ No 162,400 1 COM. EX. NoNo 0.38 0.40 0 0 ◯ No 149,300 2

TABLE 3 When 10 minutes passed from the start of casting ProductionAverage Surface Intensity of α (200) Conditions Roughness Ra (μm) Peak(cps) Supply Freely Surface in Freely Surface in of CO₂ GrindingSolidified Contact Solidified Contact with Shape in Edge Cracking byInitial Permeability No. Gas of Roll Surface with Roll Surface RollPortion Bending Test after Heat Treatment EXAMPLE Yes Yes 0.34 0.33 0 0◯ No 135,400 2 COM. EX. Yes No 0.32 0.29 430 3,100 X Yes 58,700 3 COM.EX. No No 0.81 0.85 210 2,130 ◯ Yes 75,400 4

EXAMPLES 3 and 4, COMPARATIVE EXAMPLES 5-8

An ingot of an alloy having a composition of 9 atomic % of Si W and 13atomic % of B, the balance being substantially Fe, was introduced into acrucible 1 shown in FIG. 1 and melted by induction heating by ahigh-frequency coil 2. The resultant melt 3 was ejected onto the coolingroll 5 made of a Cu—Cr alloy and rapidly quenched to produce anamorphous alloy ribbon 6 having a width of 40 mm and a thickness of 20μm under the conditions shown in Table 4.

TABLE 4 Casting Conditions Temperature of melt 3 1,300° C. Peripheralspeed of cooling roll 5 30 m/second Distance D between tip end of 180 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas40 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.08-mm-diameter brass wire brush Distance L between paddle 10 and 10 mmorifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂ gas-blowing55 mm in width direction of nozzle 9 cooling roll 5 and 1 mm in rotationdirection of cooling roll 5

Taken as samples were amorphous alloy ribbon portions obtained when 1and 10 minutes, respectively, passed from the start of casting. Thesamples of EXAMPLE 3 and COMPARATIVE EXAMPLES 5 and 6 were ribbonportions obtained when 1 minute passed from the start of casting, andthe samples of EXAMPLE 4 and COMPARATIVE EXAMPLES 7 and 8 were ribbonportions obtained when 10 minutes passed from the start of casting.

Incidentally, the grinding of the cooling roll 5 was carried out byrotating a brush 11 in the same direction as the cooling roll 5 in theproduction process of the ribbons 6 of EXAMPLES 3 and 4 in the presenceof a CO₂ gas supplied. The grinding of the cooling roll 5 was notcarried out in the production process of the ribbons 6 of COMPARATIVEEXAMPLES 5 and 7 in the presence of a CO₂ gas supplied. The grinding ofthe cooling roll 5 were also not carried out in the production processof the ribbons 6 of COMPARATIVE EXAMPLES 6 and 8 in the absence of a CO₂gas. Each of the resultant amorphous alloy ribbons 6 started to be woundaround a reel 8 after about 2 seconds from the start of casting in thesame manner as in EXAMPLE 1.

Each of the amorphous alloy ribbons of EXAMPLE 3 and COMPARATIVEEXAMPLES 5 and 6 were evaluated with respect to surface roughness, acrystal phase, embrittlement and a shape in edge portions in the samemanner as in EXAMPLE 1. The evaluation results are shown in Tables 5 and6. As is clear from Table 5, regardless of whether or not the grindingof the cooling roll 5 was carried out, the amorphous alloy ribbonportions of EXAMPLE 3 and COMPARATIVE EXAMPLE 5 obtained when 1 minutepassed from the start of casting with a CO₂ gas supplied hadsubstantially the same surface roughness, which was smaller than thesurface roughness of the ribbon of COMPARATIVE EXAMPLE 6 producedwithout supplying a CO₂ gas. With respect to embrittlement,crystallization and a shape in edge portions, there were no appreciabledifferences among the ribbons of EXAMPLE 3 and COMPARATIVE EXAMPLES 5and 6.

As shown in Table 6, among the amorphous alloy ribbon portions obtainedwhen 10 minutes passed from the start of casting, the ribbon portions ofEXAMPLE 4 and COMPARATIVE EXAMPLE 7 produced while supplying a CO₂ gashad smaller surface roughness than the ribbon portions of COMPARATIVEEXAMPLE 8 produced without supplying a CO₂ gas, regardless of whether ornot the grinding of the cooling roll 5 was carried out. With respect tocrystallization and embrittlement, there were no appreciable differencesamong the ribbons of EXAMPLE 4 and COMPARATIVE EXAMPLES 7 and 8. Thisseems to be because the alloys used in EXAMPLE 4 and COMPARATIVEEXAMPLES 7 and 8 had higher capability of forming an amorphous structurethan the alloy used in EXAMPLE 1

However, the ribbon of COMPARATIVE EXAMPLE 7 produced while supplying aCO₂ gas without grinding the cooling roll 5 had a poor shape in its edgeportions. FIGS. 6 and 7 are electron photomicrographs showing the ribbonshapes of EXAMPLE 4 and COMPARATIVE EXAMPLE 7 in their edge portions. Itwas found from FIGS. 6 and 7 that the ribbon of EXAMPLE 4 had animproved shape in edge portions than the ribbon of COMPARATIVE EXAMPLE7.

TABLE 5 When 1 minute passed from the start of casting Average SurfaceIntensity of α (200) Roughness Ra (μm) Peak (cps) Production ConditionsFreely Surface in Freely Surface in Shape in Cracking by Supply ofGrinding of Solidified Contact Solidified Contact Edge Bending No. CO₂Gas Roll Surface with Roll Surface with Roll Portion Test EXAMPLE YesYes 0.26 0.22 0 0 ◯ No 3 COM. EX. Yes No 0.25 0.21 0 0 ◯ No 5 COM. EX.No No 0.36 0.31 0 0 ◯ No 6

TABLE 6 When 10 minutes passed from the start of casting ProductionsAverage Surface Intensity of α (200) Conditions Roughness Ra (μm) Peak(cps) Supply of Grinding Freely Surface in Freely Surface in Shape inCracking by CO₂ of Solidified Contact Solidified Contact Edge BendingNo. Gas Roll Surface with Roll Surface with Roll Portion Testhz,1/48EXAMPLE Yes Yes 0.31 0.30 0 0 ◯ No 4 COM. EX. Yes No 0.30 0.32 0 0 X No7 COM. EX. No No 0.61 0.65 0 0 ◯ No 8

EXAMPLES 5-7

Each ingot of alloys having compositions shown in Table 8 was introducedinto a crucible 1 shown in FIG. 1, and melted by induction heating by ahigh-frequency coil 2. Each of the resultant alloy melts 3 was ejectedonto a cooling roll 5 made of a Cu—Be alloy and rapidly quenched toproduce an amorphous alloy ribbon 6 having a width of 30 mm and athickness of 22 μm under the conditions shown in Table 7. The casting ofthe amorphous alloy ribbon was repeated 10 times. In the productionprocess of the ribbon with a CO₂ gas supplied, the grinding of thecooling roll 5 was carried out by rotating a brush 11 in the samedirection as the cooling roll 5. The winding method of the resultantribbon was the same as in EXAMPLE 1.

TABLE 7 Casting Conditions Temperature of melt 3 1,350° C. Peripheralspeed of cooling roll 5 27 m/second Distance D between tip end of 120 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas30 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.06-mm-diameter stainless steel wire brush Distance L between paddle 10and 15 mm orifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂gas-blowing 40 mm in width direction of nozzle 9 cooling roll 5 and 1 mmin rotation direction of cooling roll 5

Each of the resultant ribbons was measured with respect to an averagesurface roughness Ra according to JIS B 0601 both on a freely solidifiedsurface and on a side in contact with the cooling roll 5. Also, a 180°bending test was carried out according to JIS Z 2248 to evaluate thepercentage of cracking in each sample. The percentage of cracking wasdetermined on 10 samples for each composition as a ratio of samples withcracking to all samples, each sample being a ribbon portion obtained 10minutes after the start of casting. The results are shown in Table 8. Asis clear from Table 8, the average surface roughness Ra was as small as0.5 μm or less in any samples, though the ribbon of EXAMPLE 7 containingmore than 13 atomic % of B became brittle. The observation of ribbonedge shapes by an electron micrograph revealed that no ribbons sufferedserrated irregularities in their edge portions.

TABLE 8 Average Surface Roughness Ra (μm) Freely Surface in CompositionSolidified Contact Cracking No. (at. %) Surface with Roll (%) EXAMPLEFe_(bal.)Nb₄Si₅B₉ 0.38 0.37 0 5 EXAMPLE Fe_(bal.)Nb₄Si₅B₁₂ 0.35 0.38 0 6EXAMPLE Fe_(bal,)Nb₄Si₅B₁₆ 0.37 0.36 60 7

Each of the amorphous alloy ribbons of EXAMPLES 5 and 6 was heat-treatedunder the same conditions as in EXAMPLE 1 except for the heat treatmenttemperature of 600-650° C. The observation of each heat-treated ribbonby a transmission electron micrograph revealed that any of theheat-treated ribbons had a nano-crystalline structure containing finecrystals having an average particle size of 100 nm or less. It wasconfirmed from these results that these amorphous alloy ribbons wereconverted to nano-crystalline alloy ribbons by a heat treatment.

EXAMPLES 8-19

An ingot of an alloy having a composition shown in Table 10 wasintroduced into a crucible 1 shown in FIG. 1, and melted by inductionheating by a high-frequency coil 2. Each of the resultant alloy melts 3was ejected onto a cooling roll 5 made of a Cu—Be alloy and rapidlyquenched to produce an amorphous alloy ribbon 6 having a width of 40 mmand a thickness of 20 μm under the conditions shown in Table 9 below. Inthe production process of the ribbon 6 with a CO₂ gas supplied, thegrinding of the cooling roll 5 was carried out by rotating a brush 11 inthe same direction as the cooling roll 5. The winding method of theresultant ribbon was the same as in EXAMPLE 1.

TABLE 9 Casting Conditions Temperature of melt 3 1,350° C. Peripheralspeed of cooling roll 5 27 m/second Distance D between tip end of 120 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas30 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.07-mm-diameter brass wire brush Distance L between paddle 10 and 15 mmorifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂ gas-blowing40 mm in width direction of nozzle 9 cooling roll 5 and 1 mm in rotationdirection of cooling roll 5

Using as samples amorphous alloy ribbon portions obtained when 20minutes passed from the start of casting, the peak of an α-Fe crystalphase on a side in contact with the cooling roll 5 was evaluated byX-ray diffraction. As a result, it was confirmed that any of theamorphous alloy ribbons had no precipitated crystal phase.

Each sample of the amorphous alloy ribbons was wound around a reel 8 toform a wound core having an outer diameter of 19 mm and an innerdiameter of 15 mm, which was heat-treated by keeping at 500-600° C. for1 hour and then cooling. The observation of the heat-treated ribbons bya transmission electron micrograph revealed that any of the heat-treatedribbons had a nano-crystalline structure containing fine crystals havingan average particle size of 100 nm or less. No irregular edge shapeswere observed in any amorphous alloy ribbons.

Each nano-crystalline alloy ribbon was measured with respect to themaximum value of a specific initial permeability μ_(i) at a frequency of1 kHz. As a result, it was found that the ribbons having compositionswith the most preferred range of B in EXAMPLES 8-17 had as high aspecific initial permeability μ_(i) as 80,500-128,000 at 1 kHz, and thatthe ribbons of EXAMPLES 18 and 19 containing more than 10 mol % of B hadas low a specific initial permeability μ_(i) as 47,000 and 35,000,respectively, at 1 kHz.

TABLE 10 Composition Maximum Value of Specific No. (mol %) InitialPermeability μ_(i) at 1 kHz EXAMPLE Fe_(bal.)Cu_(0.75)Au_(0.15)Nb₃Si₁₅B₈98,000 8 EXAMPLE Fe_(bal.)Cu₁Nb₃Si₁₅B_(8.5) 128,000 9 EXAMPLEFe_(bal)Cu₁Mo₃Si₁₅B₈ 108,000 10 EXAMPLE Fe_(bal.)Cu₁Mo₃Si₁₅B_(8.5)111,000 11 EXAMPLE Fe_(bal.)Cu_(0.6)Nb_(2.6)Si₁₁B₉ 98,500 12 EXAMPLEFe_(bal.)Cu_(0.6)Nb_(2.6)Si₁₂B₉ 109,000 13 EXAMPLEFe_(bal.)Cu_(0.9)Nb₂Mo₁Si₁₄B₉ 92,300 14 EXAMPLEFe_(bal.)Cu_(0.9)Nb₂Mo₁Si₁₄B_(9.1) 91,500 15 EXAMPLEFe_(bal.)Cu₁Nb_(3.5)Zr_(3.5)B₈ 85,500 16 EXAMPLEFe_(bal.)Cu₁Nb_(3.5)Zr_(3.5)B_(8.5) 80,500 17 EXAMPLEFe_(bal.)Cu_(0.75)Au_(0.1)Nb₃Si₁₅B₁₂ 47,000 18 EXAMPLEFe_(bal.)Cu_(0.75)Au_(0.1)Nb₃Si₁₅B₁₄ 35,000 19

EXAMPLES 20 and 21, COMPARATIVE EXAMPLE 9

An ingot of an alloy having a composition ofCu₁Nb_(2.5)Si_(13.5)B₇Fe_(bal.) by atomic % was introduced into acrucible 1 shown in FIG. 1, and melted by induction heating by ahigh-frequency coil 2. The resultant alloy melt 3 was ejected onto acooling roll 5 made of a Cu—Be alloy under the conditions shown in Table11 and rapidly quenched, to produce an amorphous alloy ribbon 6 having awidth of 30 mm and a thickness of 19 μm. In the production process ofthe amorphous alloy ribbon 6 of EXAMPLE 20, the grinding of the coolingroll 5 was carried out by rotating a brush 11 in the same direction asthe cooling roll 5 while supplying a CO₂ gas. The winding method of theresultant ribbon was the same as in EXAMPLE 1. The casting was repeated10 times under the same conditions.

TABLE 11 Casting Conditions Temperature of melt 3 1,350° C. Peripheralspeed of cooling roll 5 27 m/second Distance D between tip end of 120 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas30 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.06-mm-diameter stainless steel wire brush Distance L between paddle 10and 15 mm orifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂gas-blowing 40 mm in width direction of nozzle 9 cooling roll 5 and 1 mmin rotation direction of cooling roll 5

The amorphous alloy ribbon 6 of EXAMPLE 21 was produced under the sameconditions as in EXAMPLE 20 except for supplying a CO₂ gas at a flowrate of 30 L/minute since before the start of casting. The amorphousalloy ribbon 6 of COMPARATIVE EXAMPLE 9 was produced under the sameconditions as in EXAMPLE 20 except for supplying no CO₂ gas at all. InEXAMPLE 21 and COMPARATIVE EXAMPLE 9, too, the casting was repeated 10times.

Winding around a reel 8 was 100% success in the amorphous alloy ribbonof EXAMPLE 20 produced by starting to supply a CO₂ gas near a paddle ofthe alloy melt after 5 seconds from the start of casting, and in theamorphous alloy ribbon of COMPARATIVE EXAMPLE 9 produced withoutsupplying a CO₂ gas, though success was as low as 10% in winding arounda reel 8 in the amorphous alloy ribbon of EXAMPLE 21 produced bysupplying a CO₂ gas since before the start of casting. However, theamorphous alloy ribbon of COMPARATIVE EXAMPLE 9 was poor in surfaceroughness.

The amorphous alloy ribbon of EXAMPLE 20 was heat-treated under the sameconditions as in EXAMPLE 1, and observed by a transmission electronmicrograph. As a result, it was found that it had a nano-crystallinestructure having fine crystals having an average particle size of 100 nmor less. It was thus confirmed that this amorphous alloy ribbon wasturned to a nano-crystalline alloy ribbon by a heat treatment.

EXAMPLES 22 and 23

An ingot of an alloy having a composition of Si₉B₁₃Fe_(bal.) by atomic %was introduced into a crucible 1 shown in FIG. 1, and melted byinduction heating by a high-frequency coil 2. The resultant alloy meltwas ejected onto a cooling roll 5 made of a Cu—Be alloy and rapidlyquenched, to produce an amorphous alloy ribbon 6 having a width of 40 mmand a thickness of 20 μm under the conditions shown in Table 12 below.The grinding of the cooling roll 5 was carried out by rotating agrinding brush 11 in the same direction as the cooling roll 5. Thewinding method of the resultant ribbon was the same as in EXAMPLE 1. Thecasting was repeated 10 times under the same conditions.

TABLE 12 Casting Conditions Temperature of melt 3 1,300° C. Peripheralspeed of cooling roll 5 30 m/second Distance D between tip end of 180 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas40 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.06-mm-diameter stainless steel wire brush Distance L between paddle 10and 15 mm orifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂gas-blowing 40 mm in width direction of nozzle 9 cooling roll 5 and 1 mmin rotation direction of cooling roll 5

The amorphous alloy ribbon 6 of EXAMPLE 23 was produced under the sameconditions as in EXAMPLE 22 except for supplying a CO₂ gas at a flowrate of 30 L/minute since before the start of casting. In EXAMPLE 23,too, the casting was repeated 10 times under the same conditions.

100% success was achieved in winding around a reel 8 in the amorphousalloy ribbon of EXAMPLE 22 produced by starting to supply a CO₂ gas neara paddle of the alloy melt after 5 seconds from the start of casting. Onthe other hand, the percentage of success in winding was only 20% in thecase of the amorphous alloy ribbon of EXAMPLE 23 produced under theconditions of continuing supplying a CO₂ gas from before the start ofcasting. It was thus found that by starting the supply of a CO₂ gasafter 5 seconds from the start of casting, the resultant amorphous alloyribbon was highly likely to be wound without breakage.

EXAMPLES 24 and 25

An ingot of an alloy having a composition ofFe_(1.3)Mn_(3.7)Mo_(2.5)Si₁₅B₉Co_(bal.) by atomic % was introduced intoa crucible 1 shown in FIG. 1, and melted by induction heating by ahigh-frequency coil 2. The resultant alloy melt 3 was ejected onto acooling roll 5 made of a Cu—Be alloy and rapidly quenched to produce anamorphous alloy ribbon 6 of having a width of 40 mm and a thickness of16 μm under the conditions shown in Table 13 below. The grinding of thecooling roll 5 was carried out by rotating the grinding brush 11 in thesame direction as the cooling roll 5. The winding method of theresultant ribbon was the same as in EXAMPLE 1.

TABLE 13 Casting Conditions Temperature of melt 3 1,250° C. (meltingpoint of alloy: 1050° C.) Peripheral speed of cooling roll 5 30 m/secondDistance D between tip end of 160 μm melt-ejecting nozzle 4 and coolingroll 5 Position of CO₂ gas-blowing nozzle On upstream side ofmelt-ejecting 9 nozzle 4 with CO₂ gas blown in radial direction ofcooling roll 5 (see FIG. 2) Flow rate of CO₂ gas 40 L/minute Start ofsupplying CO₂ gas After 5 seconds from start of casting Grinding ofcooling roll 5 Grinding at peripheral speed of 5 m/second fromimmediately after start of casting to end of casting with0.08-mm-diameter brass wire brush Distance L between paddle 10 and 20 mmorifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂ gas-blowing50 mm in width direction of nozzle 9 cooling roll 5 and 1.5 mm inrotation direction of cooling roll 5

The amorphous alloy ribbon 6 of EXAMPLE 25 was produced under the sameconditions as in EXAMPLE 24 except for setting the peripheral speed ofthe cooling roll 5 at 40 m/second. However, the melt-ejecting nozzle 4was provided with a large slit in EXAMPLE 25 to make the ribbonthickness substantially the same as in EXAMPLE 24.

Taken as samples from the ribbons of EXAMPLES 24 and 25 were portionsobtained when 8 minutes passed from the start of casting, and theiraverage surface roughness Ra was measured according to JIS B 0601 bothon a freely solidified surface and on a side in contact with the coolingroll 5. The measurement results are shown in Table 14. It is clear fromTable 14 that the surface roughness of the ribbon on a side in contactwith the cooling roll 5 was susceptible to influence by the peripheralspeed of the cooling roll 5.

TABLE 14 Average Surface Roughness Ra (μm) Peripheral Freely Surface inSpeed of Supply of Solidified Contact No. Cooling Roll CO₂ Gas Surfacewith Roll EXAMPLE 30 Yes 0.37 0.29 24 EXAMPLE 40 Yes 0.57 0.46 25

The ribbon edge shape of each amorphous alloy was observed by a scanningelectron micrograph. The results are shown in FIGS. 8 and 9. It wasfound from FIGS. 8 and 9 that the ribbon produced under the conditionsthat the peripheral speed of the cooling roll 5 was 40 m/second hadlarger irregularity in edge shapes than the ribbon produced under theconditions that the peripheral speed of the cooling roll 5 was 30m/second. Incidentally, no irregularity was observed in edge shapes inthe ribbon obtained without supplying a CO₂ gas.

EXAMPLES 26-29, COMPARATIVE EXAMPLE 10

An ingot of an alloy having a composition ofCu₁Nb_(2.5)Si_(13.5)B₇Fe_(bal.) by atomic % was introduced into acrucible 1 shown in FIG. 1, and melted by induction heating by ahigh-frequency coil 2. The resultant alloy melt 3 was ejected onto acooling roll 5 made of a Cu—Be alloy and rapidly quenched, to produceamorphous alloy ribbons of EXAMPLES 26-29 each having a width of 35 mmand a thickness of 18.5 μm under the conditions shown in Table 15 below.The grinding of the cooling roll 5 was carried out by rotating thegrinding brush 11 in the same direction as the cooling roll 5. Thewinding method of the resultant ribbon was the same as in EXAMPLE 1.

TABLE 15 Casting Conditions Temperature of melt 3 1,230° C., 1,300° C.,1,390° C. (melting point of alloy: 1,150° C.) Peripheral speed ofcooling roll 5 30 m/second Distance D between tip end of 150 μmmelt-ejecting nozzle 4 and cooling roll 5 Position of CO₂ gas-blowingnozzle On upstream side of melt-ejecting 9 nozzle 4 with CO₂ gas blownin radial direction of cooling roll 5 (see FIG. 2) Flow rate of CO₂ gas32 L/minute Start of supplying CO₂ gas After 5 seconds from start ofcasting Grinding of cooling roll 5 Grinding at peripheral speed of 5m/second from immediately after start of casting to end of casting with0.08-mm-diameter brass wire brush Distance L between paddle 10 and 15 mmorifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂ gas-blowing45 mm in width direction of nozzle 9 cooling roll 5 and 2 mm in rotationdirection of cooling roll 5

Though the production of an amorphous alloy ribbon was attempted inCOMPARATIVE EXAMPLE 10 under the same conditions as in EXAMPLE 26 exceptfor setting the temperature of an alloy melt at 1,130° C., a nozzle wasclogged after several seconds from the start of casting, failing toobtain an amorphous alloy ribbon. In addition, the amorphous alloyribbon 6 of EXAMPLE 29 was produced under the same conditions as inEXAMPLE 26 except for setting the temperature of an alloy melt at 1,430°C.

Taken as samples from the resultant four types of amorphous alloyribbons of EXAMPLES 26-29 were portions obtained when 8 minutes passedfrom the start of casting, and they were measured with respect to anaverage surface roughness Ra according to JIS B 0601 on a side incontact with the cooling roll 5. The results are shown in Table 16.

TABLE 16 Temperature of Alloy Ra on Surface in Contact No. Melt (° C.)with Cooling Roll (μm) EXAMPLE 1,230 0.32 26 EXAMPLE 1,300 0.29 27EXAMPLE 1,390 0.33 28 EXAMPLE 1,430 0.51 29

As is clear from Table 16, three types of amorphous alloy ribbons ofEXAMPLES 26-28 cast from the alloy melts at preferred temperatures hadan average surface roughness Ra of as small as less than 0.4 μm, theamorphous alloy ribbon of EXAMPLE 29 cast from the alloy melt at 1,430°C. had an average surface roughness Ra of 0.51 μm, about 1.5 times aslarge as those of EXAMPLES 26-28.

The amorphous alloy ribbons of EXAMPLES 26-29 were heat-treated underthe same conditions as in EXAMPLE 1. The observation of the heat-treatedribbons by a transmission electron micrograph revealed that any of theheat-treated ribbons had a nano-crystalline structure containing finecrystals having an average particle size of 100 nm or less. It wasconfirmed from these results that these amorphous alloy ribbons wereconverted to nano-crystalline alloy ribbons by a heat treatment.

EXAMPLES 30 and 31

An ingot of an alloy having a composition ofCu₁Nb₃Si_(15.5)B_(6.5)Fe_(bal.) by atomic % was introduced into acrucible 1 shown in FIG. 1, and melted by induction heating by ahigh-frequency coil 2. The resultant alloy melt 3 was ejected onto acooling roll 5 made of a Cu—Be alloy and rapidly quenched to produce anamorphous alloy ribbon 6 of EXAMPLE 30 having a width of 20 mm and athickness of 15 μm under the conditions shown in Table 17 below. Thegrinding of the cooling roll 5 was carried out by rotating the grindingbrush 11 in the same direction as the cooling roll 5. The winding methodof the resultant ribbon was the same as in EXAMPLE 1.

TABLE 17 Casting Conditions Temperature of melt 3 1,350° C. (meltingpoint of alloy: 1,135° C.) Peripheral speed of cooling roll 5 25m/second Distance D between tip end of 120 μm melt-ejecting nozzle 4 andcooling roll 5 Position of CO₂ gas-blowing nozzle On upstream side ofmelt-ejecting 9 nozzle 4 with CO₂ gas blown in radial direction ofcooling roll 5 (see FIG. 2) Flow rate of CO₂ gas 40 L/minute Start ofsupplying CO₂ gas After 5 seconds from start of casting Grinding ofcooling roll 5 Grinding at peripheral speed of 5 m/second fromimmediately after start of casting to end of casting with0.06-mm-diameter stainless steel wire brush Distance L between paddle 10and 25 mm orifice of CO₂ gas-blowing nozzle 9 Shape of orifice of CO₂gas-blowing 30 mm in width direction of nozzle 9 cooling roll 5 and 1 mmin rotation direction of cooling roll 5

The amorphous alloy ribbon 6 of EXAMPLE 31 was also produced under thesame conditions as in EXAMPLE 30 except for setting the distance Dbetween the tip end of the melt-ejecting nozzle 4 and the cooling roll 5at 250 μm. In this case, the melt-ejecting nozzle 4 was provided with asmall slit such that the thickness of the ribbon was substantially equalto that in EXAMPLE 30.

The ribbons of EXAMPLES 30 and 31 were measured with respect to anaverage surface roughness Ra according to JIS B 0601 both on a freelysolidified surface and on a side in contact with the cooling roll 5. Theresults are shown in Table 18. As is clear from Table 18, when thedistance D between the tip end of the melt-ejecting nozzle 4 and thecooling roll 5 was as small as 200 μm or less, the resultant amorphousalloy ribbon had small surface roughness.

Each of the amorphous alloy ribbons of EXAMPLES 30 and 31 was wound in atoroidal form to produce a wound core having an outer diameter 19 mm andan inner diameter of 15 mm. Each wound core was heat-treated at 520° C.for 1 hour in a non-reactive atmosphere to obtain a wound core of anano-crystalline alloy ribbon having a nano-crystalline structurecontaining fine crystals having an average particle size of 100 nm orless.

Each wound core was provided with a primary winding of 10 turns and asecondary winding of 10 turns to measure a maximum permeability μ_(max)at 50 Hz. The results are also shown in Table 18. It was found fromTable 18 that high permeability was obtained in a wound core formed bythe nano-crystalline alloy ribbon of EXAMPLE 30 having a small averagesurface roughness Ra both on a freely solidified surface and a surfacein contact with the cooling roll 5.

TABLE 18 Distance L Ra (μm) between Tip End Freely Surface in Maximum ofNozzle and Supply of Solidified Contact Permeability No. Cooling Roll(μm) CO₂ Gas Surface with Roll μ_(max) at 50 Hz EXAMPLE 120 Yes 0.310.32 744,000 30 EXAMPLE 250 Yes 0.47 0.50 599,000 31

As described above in detail, the present invention has solved bygrinding a cooling roll the problems of the embrittlement andcrystallization of amorphous alloy ribbons and the irregular shapes intheir edge portions occurring when they are mass-produced whilesupplying a CO₂ gas. Accordingly, the method of the present inventioncan continuously produce amorphous alloy ribbons substantially free fromembrittlement, crystallization and irregular shapes in their edgeportions without breakage. In addition, the amorphous alloy ribbonsproduced by the method of the present invention can be converted tonano-crystalline alloy ribbons having excellent magnetic properties by aheat treatment.

What is claimed is:
 1. A method for producing an amorphous alloy ribbonby ejecting an alloy melt onto a cooling roll and rapidly quenching it,said amorphous alloy ribbon continuously produced in one casting stephaving the total length of 3,000 m or more, comprising grinding saidcooling roll while supplying a gas based on CO₂ near a paddle of saidalloy melt ejected onto said cooling roll so as to keep an averagesurface roughness Ra of 0.5 μm or less and a ten-point average surfaceroughness Rz of 4 μm or less during the casting when the surfaceroughness of said cooling roll is measured by a method according to JISB
 0601. 2. The method for producing an amorphous alloy ribbon accordingto claim 1, wherein the grinding of said cooling roll is carried outwith a brush.
 3. The method for producing an amorphous alloy ribbonaccording to claim 1, wherein an alloy melt comprising 13 atomic % orless of B and 15 atomic % or less of at least one element selected fromthe group consisting of transition elements of Groups 4A, 5A and 6A, thebalance being substantially Fe, is ejected onto said cooling roll andrapidly quenched.
 4. The method for producing an amorphous alloy ribbonaccording to claim 1, wherein said alloy melt contains 3 atomic % orless of at least one of Cu, Ag and Au.
 5. The method for producing anamorphous alloy ribbon according to claim 1, wherein said gas based onCO₂ starts to be supplied near a paddle of said alloy melt after thesurface temperature of said cooling roll has become substantiallyconstant.
 6. The method for producing an amorphous alloy ribbonaccording to claim 1, wherein said ribbon is cast under the conditionsthat the peripheral speed of said cooling roll is 35 m/second or less,that the temperature of said melt is from the melting point of its alloy+50° C. to the melting point of its alloy +250° C., and that a distancebetween a tip end of a melt-ejecting nozzle and said cooling roll is 200μm or less.
 7. The method for producing an amorphous alloy ribbonaccording to claim 6, wherein the peripheral speed of said cooling rollis 20-30 m/second.
 8. The method for producing an amorphous alloy ribbonaccording to claim 1, wherein an amorphous alloy ribbon having athickness of 8-25 μm is produced.
 9. A method for producing anano-crystalline alloy ribbon comprising heat-treating said amorphousalloy ribbon recited in claim 1 at a temperature equal to or higher thanthe crystallization temperature of said alloy, to form nano-crystallinestructure having an average particle size of 100 nm or less.
 10. Amethod for producing an amorphous alloy ribbon by ejecting an alloy meltonto a cooling roll and rapidly quenching it, said amorphous alloyribbon continuously produced in one casting step having the total lengthof 3,000 m or more, comprising (a) preparing an alloy melt having acomposition comprising 13 atomic % or less of B and 15 atomic % or lessof at least one element selected from the group consisting of transitionelements of Groups 4A, 5A and 6A, the balance being substantially Fe;(b) ejecting said alloy melt at a temperature from the melting point ofsaid alloy +50° C. to the melting point of said alloy +250° C. through anozzle onto said cooling roil rotating at a peripheral speed of 35m/second or less, a distance between a tip end of said nozzle and saidcooling roll being 200 μm or less; (c) starting to supply a gas based onCO₂ to said alloy melt after the surface temperature of said coolingroll has become substantially constant; and (d) grinding said coolingroil while supplying said gas based on CO₂.